define(function(){
  (function (doc, win) {
          var docEl = doc.documentElement,
              resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
              recalc = function () {
                  var clientWidth = docEl.clientWidth;
                  if (!clientWidth) return;
                  if(clientWidth>=640){
                      docEl.style.fontSize = '100px';
                  }else{
                      docEl.style.fontSize = 100 * (clientWidth / 640) + 'px';
                  }
              };

          if (!doc.addEventListener) return;
          win.addEventListener(resizeEvt, recalc, false);
          doc.addEventListener('DOMContentLoaded', recalc, false);
      })(document, window);
})
